Audio amplifiers are used in many known designs in music systems, e.g. for home use or to provide music in movie theaters, discotheques, etc., or in public address systems which are used e.g. in public buildings, schools, universities, etc. to disseminate announcements. Audio amplifiers of that type can be based on any type of amplifier principle and are all based on the principle of converting an input signal into an amplified output signal.
Standards now govern the output interfaces of audio amplifiers, however, wherein two different technologies for implementing the standards are currently in use. The two technologies differ in terms of how the electromechanical acoustic signal transformers are supplied with the output signal.
On the one hand, low-impedance operation of audio amplifiers is known, wherein the audio amplifier is a low ohmic, controlled voltage source and directly drives the connected loudspeakers and electromechanical acoustic signal transformers. When used in public address systems in large buildings or spaces, however, this technology often requires that the cross section of the loudspeaker lead be disproportionately large, due to the currents that are required and the length of the loudspeaker leads.
In applications of this type in particular, a different technology is utilized, e.g. high-impedance operation, which is also known as 100-volt technology. According to this technology, the output signal of the audio amplifier is transformed to 100 volts using a low-frequency transmitter and, as in the case with energy distribution networks at this voltage level, are transmitted to a plurality of loudspeakers connected in parallel. Each loudspeaker has a separate transmitter or transformer for adjusting the voltage and impedance. The advantage of the technology is that loudspeaker leads having a small cross section can be used for power supply, the public address system can be expanded very easily by connecting additional loudspeakers in parallel, and the loudness level of individual loudspeakers can be adjusted by tapping into the transmitter or transformer in the loudspeaker. High-impedance systems are not limited to a voltage level of 100 volts; a voltage level of 70 volts is also common, for instance.